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    <p>specifying <code>dot[Real]</code> explicitly should work too. </p> <pre><code>def rowDot(r1: Row, r2: Row) = dot[Real](_*_)(r1, r2) </code></pre> <p><strong>EDIT</strong></p> <p>replying to your edit: I think the issue is that the implicit conversion from <code>Array</code> to <code>WrappedArray</code> is not applied recursively when you have a <code>Array[Array]</code>. </p> <p><code>Array[Int]</code> is not an <code>Iterable[Int]</code>; normally, when you assign it to a Iterable, an <code>Array[Int]</code> is implicitly converted to a <code>WrappedArray[Int]</code> (where <code>WrappedArray</code> <strong>is</strong> a Iterable[Int]). This is what happens when you use <code>List[Array[Int]]</code> (you get a <code>List[WrappedArray[Int]]</code> implicitly). </p> <p>However, as I said, the implicit conversion is not applied recursively, so an <code>Array[Array[Int]]</code> is not implicitly converted to <code>WrappedArray[WrappedArray[Int]]</code>.</p> <p>Here's a REPL session that demonstrates the problem:</p> <p>A List[Array[Int]] can be assigned to Iterable[Iterable[Int]] (note that Array is converted to WrappedArray) </p> <pre><code>scala&gt; val i : Iterable[Iterable[Int]] = List(Array(1,2), Array(1,2,3)) i: Iterable[Iterable[Int]] = List(WrappedArray(1, 2), WrappedArray(1, 2, 3)) </code></pre> <p>An Array[Array[Int]] does not work automatically (as you discovered)</p> <pre><code>scala&gt; val j : Iterable[Iterable[Int]] = Array(Array(1,2), Array(1,2,3)) &lt;console&gt;:9: error: type mismatch; found : Array[Array[Int]] required: Iterable[Iterable[Int]] val j : Iterable[Iterable[Int]] = Array(Array(1,2), Array(1,2,3)) ^ </code></pre> <p>However, with some hand-holding (converting manually the inner Arrays to WrappedArrays) everything works again: </p> <pre><code> scala&gt; import scala.collection.mutable.WrappedArray import scala.collection.mutable.WrappedArray scala&gt; val k : Iterable[Iterable[Int]] = Array(WrappedArray.make(Array(1,2)), WrappedArray.make(Array(1,2,3))) k: Iterable[Iterable[Int]] = WrappedArray(WrappedArray(1, 2), WrappedArray(1, 2, 3)) </code></pre>
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    1. COThanks for you answer, and also the clarification about Array's and Iterable's. The fact that Array isn't iterable seems odd -- is this a necessary consequence of representing arrays as Java arrays?
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    2. COyes, it's for interoperability with java. Scala has kept java types and implicitly converts them to their scala richer counterparts (see also string for another example)
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